Fluid meters, such as Coriolis flow meters, vibrating densitometers, piezoelectric flow meters, etc. typically include one or more tubes for containing a fluid. The fluid may be flowing such as in a Coriolis flow meter or stationary such as in a vibrating densitometer. The fluid may comprise a liquid, a gas, or a combination thereof. In some situations, the fluid may include suspended particulates. Typically, the fluid tubes are enclosed in a case in order to protect the tubes and associated electrical components as well as provide a more stable environment.
In many situations, a portion of the fluid tubes extend out of the case and are joined to a pipeline interface, such as a manifold. The fluid tubes are generally joined to the manifold by welding. The manifolds are then typically brazed to case ends in a vacuum brazing operation. Once the appropriate electrical sensors are attached to the fluid tubes, the case ends are then welded to the case. Flanges are then generally welded to the case ends or the manifold in order to subsequently couple the fluid meter to the pipeline carrying a process fluid.
Obtaining adequate and reliable connections between the various components is often a problem with prior art fluid meters. One reason is due to thermal expansion of the materials used for the various components of the fluid meter. As the components are being coupled to one another, high temperatures are often involved, which can result in significant changes in the components' dimensions. This is especially true when the various components comprise metals that are coupled by welding, brazing, soldering, etc., which can require an excessive amount of heat. While this may not create a problem if all of the components are formed from the same material or materials with similar coefficients of thermal expansion as the components will expand and contract in unison, this is not always feasible. In many situations, the fluid tubes are formed from a different material than the case, the case ends, and the flanges. For example, when the process fluid in the fluid meter comprises a highly corrosive fluid, the fluid tubes need to be formed from a material that is highly corrosion resistant, such as titanium, tantalum, or zirconium. Similarly, any other portion of the wetted path should also be formed from high corrosion resistant materials. For example, in a dual fluid tube meter, the manifold is included in the wetted fluid path. Therefore, the manifold would also need to be formed from a highly corrosion resistant material. While the case, the case ends, and the flanges would ideally be formed from the same material as the fluid tubes and the manifold, such an approach is typically cost prohibitive as titanium, tantalum, and zirconium are expensive metals. Therefore, portions of the fluid meter that are not in contact with the fluid are generally made from less expensive materials, such as stainless steel.
Although the different materials used to form the fluid meter may not be a problem when the fluid meter is at or near a predetermined temperature, such as room temperature, the differences in their coefficients of thermal expansion can create serious manufacturing problems as various portions of the meter are subjected to extreme temperature variations. A similar problem can be experienced in situations where the fluid is at an extreme temperature compared to the surrounding environment resulting in the wetted fluid path being subjected to a much higher temperature. The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide an improved fluid meter that can combine various components having differing coefficients of thermal expansion without the above-mentioned drawbacks.